Lithium Hydroxide & Alkali-Aggregate Reaction

The alkali-aggregate reaction (AAR) is that alkali ions from cement orenvironment react with reactive constituents of aggregates to form expansivematerials that produce expansive stress resulting in expansion or cracking of concretestructures. Thus the use life-span of concrete building is greatly curtailed. Preventingand inhibiting AAR is one of the important domain of concrete at home and abroad.At present,there isn't the reliable method on identifying the source of siliceouscarbonate alkali-reactivity, alkali-silica reaction may be present in alkali-reactivecarbonate cherishing microcrystalline quartz; alkali-carbonate reaction may also beexistent in the destroyed structures if there is MgO in chemistry composition of theaggregate and crystalline dolomite is found through lithofacies examination. However,the reason for the deterioration used to be thought only ASR. Because the expansionmechanism of ASR is different from that of ACR, the adopted inhibition measures arealso different. Distinguishing ASR from ACR is very important in theory and inpractice. The problems have been studied in the thesis. LiOH has been used todistinguish ASR from ACR, because it can prevent ASR and promote ACR. Theprogresses of studies are as follows:Thermodynamic analysis shows that ACR is a spontaneous process, the drivingforce of the reaction weakens as reaction goes or reaction temperature rises. At 298K,when pH value of alkali solution is up to 10.6, ACR can occur, OH- concentrationneeded for ACR increases correspondingly if reaction temperature rises. At 298K,when pH value is up to 13.1, lithium hydroxide solution-carbonate reaction possiblyproduces lithium carbonate precipitation besides calcite and brucite, OH-concentration which ACR needs does not basically change as temperature rises andlithium carbonate crystal can been formed. So, the needed alkali concentration islower when ACR occurs theoretically. The speed and mechanism of ACR belong tothe realm of kinetics study. The dynamics has been studied on magnesite, dolomite'powder- lithium hydroxide solution reaction. The conclusion is that the rate of ACR iscontrolled by interface chemical reaction at the initial stage of the reaction; followingthat it is dominated by ions passing through boundary layer, the time expended by thecontrol step is shorter; it is controlled by liquid diffusion through solid product layerand the product crystallization and growth at the middle and later stage of the reaction.The whole dedolomitizated process is as follows: (Ⅰ) OH- and M+ move to dolomitecrystal surface, the defective crystal lattice is at first corroded and disintegrated by the i摘要external ions; (Ⅱ) the released CO3 ,Ca2+ leave dolomite crystal and migrate to 2-outside, at the same time OH- , M+ continue moving to dolomite crystal surface anderoding; (Ⅲ) the combination of CO3 and Ca2+ forms CaCO3, Mg2+ stays original 2-place for its slower migration rate and the hinder role of Ca2+ ions; (Ⅳ) the reactionof intrusive OH- and Mg2+ forms Mg(OH)2. The produced calcite deviates fromdolomite crystal, but brucite is formed in the original space, expansion and crackingof concrete made of carbonate may take place in the interior of aggregate or the jointof aggregate and paste for ACR according to dolomite crystal position. Theabove-mentioned basic theory study provides scientific basis and guide for betterunderstanding of ACR expansion and preventing ACR.The contrast research has been done on LiOH-silica and LiOH-carbonatereaction. The results show that the concrete made from alkali-active zeolitizationperlite doesn't produce expansion and cracking when it reacts with LiOH, theproducts of LiOH-silica reaction have definite shape and compact texture, theLiOH-silica reaction process itself can't cause expansion, so LiOH play a role oninhibiting expansion of ASR. The concrete made from alkali-active carbonate showsexpansion and cracking when it reacts with LiOH, the al...